Unit 5 The Structure of Matter

1. Unit 5 The Structure of Matter Chapter 17 The Elements and The Periodic Table

2. 17A – A Brief History of the Elements • Objectives: • Summarize the historical development of the idea of a chemical element • Describe the role of alchemy in the discovery of chemical elements • Explain how the historical problem of element symbols was solved • Identify the naturally monatomic and diatomic elements • Recognize and correctly use modern chemical symbols for elements • Assignments: Outline, Worksheet, and Section Review page 415

3. Introduction

4. Earliest Known Elements • Native minerals • Solid elements, like gold and silver that naturally occur in their pure form • Around since Bible times • Facet page 411

5. Earliest Known Elements • Ancient Greeks were the first to define elements as the basic building blocks of matter • Aristotle believed that all matter was composed of four “elements” • Air, fire, earth, and water • This model was accepted for thousands of years • Alchemy • Included aspects of chemistry, philosophy, religion, metallurgy, medicine and art • Acquired mystical and magical characteristics that often resulted in disreputable and harmful activities • Alchemists • Viewed as dishonest, shifty, greedy, or deluded because, for many of them, their main objective was to find ways to turn valueless materials like lead into gold • Many were serious • Discovered and purified man substances that were later understood to be chemical elements

6. Earliest Known Elements • Developed a complex system of symbols to describe their work • Different alchemist developed their own symbols often to hid their knowledge from other • This made sharing information very difficult

7. Studying Elements in the 17th and 18th Centuries • Alchemy was transformed into a real science in the 17th and 18th centuries by men like: • Isaac Newton • Did more for chemistry than physics; however, his work in physics immortalized him as one of the world’s greatest physicists • Robert Boyle • Known for Boyle’s law • Concluded that many substances could not be composed of Aristotle’s elements • Antoine Lavoisier • Dealt the death blow to Aristotle’s elements when he broke water down into hydrogen and oxygen • First to define an element as a simple chemical substance that could not be broken down into simpler substances by chemical analysis • They believed that scientific knowledge was gained by observing, experimenting, and reasoning • By the end of the 18th century 32 modern elements were known, but symbols were still difficult to memorize and use

8. Berzelius’s Element Notation • JonsJakob Berzelius • Swedish chemist and educator • Firmly established Dalton’s atomic theory • Introduced the modern system of element notation • Used the first one or two letters of an element’s Latin name • Quickly accepted by most European scientists • Essentially the same as the one used today • Discovered thorium, selenium, silicon, and cerium • When he died there were fifty-seven known elements

9. Modern Elements & Their Symbols • 117 elements exist today • The heaviest elements are all radioactive and have extremely short half-lives and are difficult to analyze before they decay to lighter elements • Represented by their chemical symbols • First letter is capitalized, second lowercase • PAGES 418-419, the periodic table…START TO MEMORIZE!

10. Modern Elements & Their Symbols • Most elements occur in nature combined in compounds, as masses of identical atoms, or in molecules of two or more atoms • Monatomic • Occur as single atoms • Only elements that exist naturally in this form are the noble (inert) gases • Diatomic • Naturally occur as molecules of two atoms • Seven: hydrogen, oxygen, nitrogen, flourine, chlorine, bromine, and iodine • Polyatomic • Molecules of elements that contain more than two atoms